The present invention relates generally to multi-component powdered compositions, and more specifically to packaged additives for settable powder compositions such as, but not limited to wallboard joint compound.
Walls and ceilings made from gypsum wallboard are conventionally constructed by attaching the wallboard panels to framing members or studs, and filling and coating the joints between the panels with a specially formulated paste composition called a joint compound. Joint compounds may be supplied as powdered compositions (to be mixed with water at the jobsite) or may be premixed with water at the factory to yield a ready mixed (or paste) joint compound. A paste joint compound (Taping grade) is placed within and over the joint formed by the abutting edges of the wallboard panels, and a paper reinforcing tape is embedded in the joint with the joint compound which is then permitted to dry. Alternately, the reinforcing tape may be of non-cellulose composition, but of a size and shape similar to strips of paper joint tape. Alternately, the reinforcing tape may be of a fiberglass weave requiring the use of chemically setting type joint compounds. When the joint compound is dry, a second joint compound (Topping or Finishing grade) is applied over the joint, and it too is permitted to dry. It is usually necessary for a third application of a joint compound and, after the third coat is dry, it may be lightly sanded and may be conventionally finished with a decorative material (paint, texture or wallpaper) then applied to the wall. All three coats of joint compound may alternately be done with problems such as binding of the wet mixer and overloading of the mixer motor.
There are several categories of joint compounds. Drying type compounds harden through the evaporation of water, whereas setting type joint compounds chemically react with water during the curing process. Setting type joint compounds typically use calcium sulfate hemihydrate, also known as stucco or Plaster of Paris, as a base. When water is added to the setting type powder, it reacts with the calcium sulfate hemihydrate via a hydration reaction to form an interlocking matrix of calcium sulfate dihydrate crystals. The interlocking crystal matrix gives the compound increased strength. The benefit of a setting type joint compound over a drying type is the overall strength of the finished joint, resulting in less shrinking and cracking, as well as an independence from having to wait for the joint compound to be completely dry prior to further finishing. Drying type joint compounds have the advantage of ease of use, as they typically come in a ready mixed form, with water being added and mixed by the manufacturer. A third type of joint compound combines the setting action of a calcium sulfate hemihydrate based compound with the ease of use of a ready mixed compound.
Ready mixed joint compound is typically supplied to the customer in either cardboard cartons or plastic pails in units having volumes of 3.5 to 4.5 gallons (13.25-17.03 L). Joint compound is supplied at a viscosity typically higher than what is applied at the jobsite. This allows the contractor to mix in additional water using a power drill and mixing paddle to achieve the desired application viscosity.
Ready mix joint compound production is typically accomplished by blending the wet and dry ingredients in a mixer until smooth, adjusting the viscosity to a desired level through water addition, then filling and sealing containers to be shipped to customers. This process can be disrupted by use of ingredients which thicken very rapidly and take longer periods of time to fully wet out and drop in viscosity, leaving the combined wet and dry ingredients in the mixer competing for water through the typical mixing cycle and at a higher than desired viscosity. The above process results in mechanical limitations and problems such as binding of the wet mixer and overloading of the mixer motor. The higher than desired viscosity at the completion of the mixing cycle affects the ease of pumping and moving the material out of the mixing system and through the packaging line and also interferes with the lidding and closing of the container.
It is known to provide selective performance enhancing additives to the joint compound mixture during formulation at the jobsite to enhance performance characteristics. In some cases, the set or dry time is accelerated, in others retarded. Also, viscosity and/or dust generation during sanding are characteristics that are influenced by additives to the mixture.
Thus, there are mechanical limitations on the types of raw materials that can be used within a typical wet mixing system for manufacturing ready mix. Depending on the particular product requirements, including long pre-use shelf life, fast setting, low viscosity of application and others, several options have been proposed to provide joint compounds with separated additives that enable the user to obtain enhanced or more desirable joint compound performance characteristics when the mixture is finalized just prior to application.
U.S. Pat. No. 6,476,099, incorporated by reference, discloses the addition of surfactant additives to joint compound to generate performance with improved cracking, improved shrinkage and reduction of surface finish defects after application to wallboard surfaces. U.S. Pat. Nos. 6,228,163 and 5,746,822 incorporated by reference, disclose joint compounds formulated with a base joint compound that is relatively inert until an extra additive is provided, functionally serving as an activator.
U.S. Pat. No. 8,822,566, incorporated by reference, discloses providing a nonhomogeneous formulation of an additive with a ready mix base joint compound for ultimate mixing by the user on the jobsite. There is an ongoing need for providing additives in a format that enables the user to adjust the operational characteristics of the joint compound to suit the particular situation.